1. Field of the Invention
The invention relates to ozone generating apparatus.
2. Description of the Prior Art
The structure and an operation of a conventional silent discharge ozonizer will be illustrated with reference to FIG. 1.
In FIG. 1, the reference 1 designates an outer cylinder; 2 designates a metallic cylindrical grounded electrode; 3 designates a high voltage electrode tube made of a dielectric; 4 designates a high voltage electrode which closely contacts the inner surface of the high voltage electrode tube; 5 designates a bushing; 6 designates an inlet for a liquid coolant for cooling the metallic cylindrical grounded electrode 2; 7 designates an outlet thereof; 8 designates an inlet of the raw material gas; and 9 designates an outlet of the ozonized gas.
When the AC voltage (10-20 KV) is applied to the high voltage electrode 4, a silent discharge is formed in the gap between the high voltage electrode tube 3 and the metallic cylindrical grounded electrode 2. Accordingly, a part of the oxygen in the feed gas is ozonized by passing the raw material gas from the feed gas inlet 8 into the discharge gap whereby the ozonized gas is discharged from outlet 9. The feed gas is dried air or oxygen.
Only a part of the discharge energy (about 5% for air feed and about 10% for oxygen feed) is used for the formation of ozone. The other energy becomes heat loss. The yield of ozone is decreased if the heat is not effectively removed to prevent a rise of the temperature in the discharge gap. Accordingly, the outer surface of the metallic cylindrical grounded electrode 2 is cooled with a liquid coolant. It is usual to use water as the liquid coolant.
In the conventional ozone generator, in order to maintain the temperature in the discharge gap below the limit capable of ozone generation, it is necessary to have less than about 0.2 watt/cm.sup.2 of discharge density (discharge power per area of discharge). Accordingly, a large area of discharge, i.e., a rather large sized apparatus is required for practical operation.